NR 322: Scale and Resolution - PowerPoint PPT Presentation

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NR 322: Scale and Resolution. Jim Graham & Alex Daniels Fall 2010 Chapter 2. Scale. Scale is the scale of the map relative to the true size of the items on the map e.g 1:750,000 1 unit on the map is equivalent to 750,000 units on the earth Small scale vs Large scale Which number is larger

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NR 322: Scale and Resolution

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NR 322: Scale and Resolution

Jim Graham & Alex Daniels

Fall 2010

Chapter 2

Scale

• Scale is the scale of the map relative to the true size of the items on the map

• e.g 1:750,000

• 1 unit on the map is equivalent to 750,000 units on the earth

• Small scale vs Large scale

• Which number is larger

• 1 / 750,000 or 1 / 2

Misunderstood Terminology

• Small Scale = Large Extent

• Think of the divisions on the scale being small

• Miles are smaller at small scale

• Large Scale = Small Extent

• Think of the divisions on the scale being big

• Miles are larger at large scale

• Recommendation:

• Use Large Extent or Small Extent

• Use Low Resolution or High Resolution

Scale can vary on a map

• What is the scale in kilometers on a Geographic Projection map?

Scale can Vary

• What is the scale on a google earth map?

Resolution

• Resolution is the ability to resolve detail

• We mostly refer to Spatial Resolution

• For Rasters/Grids/Digital Photos this means the size of the pixels.

• What distance on the ground does one pixel represent?

30 Meters

Resolution

• High resolution is awesome, why don't we make everything 1m data or better?

• The number of pixels increases exponentially as you increase spatial res.

Resolution x 2

Pixels x 4

High Resolution ~ Big Files

• Rasters and photos can get really big really fast.

• Civilian satellites now can take satellite photos as high as 41 cm resolution

• i³ in Fort Collins has 1m Satellite Photos that take 300 Gigabytes for just one area.

Low spatial resolution

• Low resolution averages data

Accuracy and Precision

• Accuracy is how close something is to the true value

• Precision is how close of a measurement you can make

• High accuracy doesn't mean high precision